[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

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L.P.S. VAN DER GEEST
life span, a low oviposition rate and fewer female progeny. No effect could be
shown on longevity of males or on male progeny survival to larval and adult stages.
The infection may affect the performance of the predator. Heat treatments of
infected colonies had some success: eggs placed for 7 days in a chamber at 33°C and
subsequently at 27°C showed a reduced infection rate, but the disease was still not
completely eliminated. Mites emerging from these eggs still showed spores inside
their body, but it was assumed that most of these spore were dead as the majority of
the mites survived. After a number of weeks, infection rates were again high,
indicating that the heat treatment was only partially effective. However, when eggs
were placed at 33°C. and when their progeny was also kept at this temperature,
disease-free mites were obtained. It was also shown that the disease may be
horizontally transmitted, probably by cannibalism.
At this moment, no other cure exists for microsporidiosis in predatory mite
mass rearings. Anti-microsporidial compounds, such as albendazole, fumagillin,
metronidazole and nifedipine were not successful in eliminating microsporidiosis in
mass cultures of P. persimilis (Bjørnson, 1998). Therefore, efforts should be made to
keep the starting cultures of predatory mites disease-free. Heat treatment of infected
eggs, or rearing infected individuals at elevated temperatures, has been shown to
reduce disease prevalence in some cases; however, the most effective and practical
means for rearing microsporidian free predatory mites is to start a new rearing with
progeny from uninfected females.
6. OTHER DISEASES
6.1. Symptoms Ascribed to Poor Condition
In this chapter, we discuss a condition in mites that cannot be ascribed to the action
of a pathogen. In a number of instances, rectal plugs, usually in combination with
abdominal discoloration have been observed in phytoseiids (Tanigoshi, Fagerlund,
& Nishio-Wong, 1981; Bjørnson et al., 1997). This discoloration is usually
manifested as two white stripes along the dorsal sides of the body within the
Malpighian tubules. The condition is frequently found in laboratory colonies of
predatory mites and it may be a sign of poor condition of the predator. Tanigoshi
(1982), for example, considered the condition a sign of senescence. Affected mites
are often lethargic and have frequently numerous densely packed, birefringent
dumbbell-shaped bodies, mainly in the Malpighian tubules, rectum and anal atrium.
In Cheyletus eruditus, abdominal discoloration is also associated with the
occurrence of birefringent crystals in the excretory organs, especially when reared
under crowded conditions. These crystals are considered to be the normal excretory
products (Hughes, 1950) and probably consist of guanine and uric acid (McEnroe,
1961). These compounds are insoluble and are probably stored in the malpighian
tubes prior to excretion. The crystals observed in P. persimilis, however, contain
high levels of potassium, low levels of phosphorous and sulphur and traces of
chlorine, very unlike the common waste products mentioned above (Bjørnson,
1998). Large numbers of crystals in mites are especially found in laboratory mites,